Inkjet printers typically include one or a plurality of inkjet print heads, each including an array of nozzles formed on a nozzle face. The nozzles eject ink drops, the ink being provided from an ink supply through an ink path. Ink drop ejection may be controlled by suitable actuators such as piezoelectric transducers. In so-called “drop-on-demand” inkjet printers, each actuator may be selectively fired to eject a drop at a specific location on a substrate. The print heads and the substrate may be moved relatively to each other during the printing operation. In particular, the substrate may be moved stepwise along a first direction, whereas the inkjet print heads are scanned continuously along a second direction, which may be perpendicular to the first direction.
For high throughput, many inkjet printers comprise a plurality of inkjet print heads. Each print head is part of an inkjet print module. In addition to the print head, such a module features further components for the feeding and conditioning of ink, for controlling the ejection of the ink by the print head and/or for mechanical or thermal purposes. A plurality of such modules are mounted to a mounting assembly, in an adjoining relationship along a longitudinal direction of the mounting assembly, i. e. a so-called “print bar” is created. The nozzle arrays of adjacent print heads may be arranged in such a way that seamless printing over the width of a plurality of inkjet print heads is possible, i. e. the nozzle array of the entire print bar is created by a plurality of inkjet print heads but still continuous with a uniform arrangement of nozzles over the whole array.
In order to print large areas, for example in textile printing, a number of print bars may be attached to a mechanical unit, the print bars and the mechanical unit forming a print engine. The entire engine is movable with respect to the substrate. In particular, each of the print bars is dedicated to produce ink dots on the substrate having a certain colour, i.e. inks of different colours (such as cyan, magenta, yellow and black) are supplied to different print bars. The image will be the combination of dots produced by different print bars during different scans of the print engine. It is crucial that the positions of the dots of different scans exactly match in order to avoid distortions of the image or colour defects.
Furthermore, the image is constituted by a number of bands created in different scans of the print engine. Even minute inaccuracies may lead to visible “stitches” at the transition from one band to the next one.
Known inkjet printers comprising a print engine having a plurality of print bars suffer from positioning inaccuracies and therefore are prone to image defects as mentioned before.